The present invention relates to a chemically amplified resist material for use in immersion lithography and a pattern formation method using the same to be employed in fabrication process or the like for semiconductor devices.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique. Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like, and use of F2 laser lasing at a shorter wavelength of 157 nm is being examined. However, since there remain a large number of problems in exposure systems and resist materials, photolithography using exposing light of a shorter wavelength has not been put to practical use.
In these circumstances, immersion lithography has been recently proposed for realizing further refinement of patterns by using conventional exposing light (for example, see M. Switkes and M. Rothschild, “Immersion lithography at 157 nm”, J. Vac. Sci. Technol., Vol. B19, p. 2353 (2001)).
In the immersion lithography, a region in an exposure system sandwiched between a projection lens and a resist film formed on a wafer is filled with a liquid having a refractive index n (whereas n>1) and therefore, the NA (numerical aperture) of the exposure system has a value n·NA. As a result, the resolution of the resist film can be improved.
Also, in order to increase the refractive index in the immersion lithography, use of an acidic solution as the immersion liquid has been proposed (see, for example, B. W. Smith, A. Bourov, Y. Fan, L. Zavyalova, N. Lafferty, F. Cropanese, “Approaching the numerical aperture of water—Immersion Lithography at 193 nm”, Proc. SPIE, Vol. 5377, p. 273 (2004)).
Now, a pattern formation method employing the immersion lithography will be described as Conventional Example 1 with reference to FIGS. 11A through 11D.
First, a positive chemically amplified resist material having the following composition is prepared:
Base polymer: poly((norbornene-5-methylene methoxymethyl carboxylate) (50 mol %)−(maleic acid) (50 mol %)) . . . 2 g
Acid generator: triphenylsulfonium trifluoromethane sulfonate . . . 0.04 g
Quencher: triethanolamine . . . 0.002 g
Solvent: propylene glycol monomethyl ether acetate . . . 20 g
Next, as shown in FIG. 11A, the aforementioned chemically amplified resist material is applied on a substrate 1 so as to form a resist film 2 with a thickness of 0.35 μm.
Then, as shown in FIG. 11B, with water 4, that is, an immersion liquid, provided on the resist film 2, pattern exposure is carried out by irradiating the resist film 2 through the water 4 with exposing light 5 of ArF excimer laser having NA of 0.68 having passed through a mask 6.
After the pattern exposure, as shown in FIG. 11C, the resist film 2 is baked with a hot plate at a temperature of 105° C. for 60 seconds, and thereafter, the resultant resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer. In this manner, a resist pattern 2a made of an unexposed portion of the resist film 2 and having a line width of 0.09 μm is formed as shown in FIG. 11D.
Furthermore, a pattern formation method employing the immersion lithography performed with a barrier film provided on a resist film will be described as Conventional Example 2 with reference to FIGS. 12A through 12D, 13A and 13B.
First, a positive chemically amplified resist material having the following composition is prepared:
Base polymer: poly((norbornene-5-methylene2gmethoxymethyl carboxylate) (50 mol %) - (maleicanhydride) (50 mol %))Acid generator: triphenylsulfonium trifluoromethane0.04gsulfonateQuencher: triethanolamine0.002gSolvent: propylene glycol monomethyl ether acetate20g
Next, as shown in FIG. 12A, the aforementioned chemically amplified resist material is applied on a substrate 11 so as to form a resist film 12 with a thickness of 0.35 μm.
Then, as shown in FIG. 12B, by using a barrier film material having the following composition, a barrier film 13 having a thickness of 0.03 μm is formed on the resist film 12 by, for example, spin coating:
Base polymer: polyvinyl hexafluoroisopropyl alcohol 1 gSolvent: n-butyl alcohol20 g
Next, as shown in FIG. 12C, the resultant barrier film 13 is baked with a hot plate at a temperature of 120° C. for 90 seconds.
Then, as shown in FIG. 12D, with water 14, that is, an immersion liquid, provided on the barrier film 13, pattern exposure is carried out by irradiating the resist film 12 through the water 14 and the barrier film 13 with exposing light 15 of ArF excimer laser having NA of 0.68 having passed through a mask 16.
After the pattern exposure, as shown in FIG. 13A, the resist film 12 is baked with a hot plate at a temperature of 105° C. for 60 seconds, and thereafter, the resultant resist film 12 is developed with a 2.38 wt % tetramethylammonium hydroxide developer. In this manner, a resist pattern 12a made of an unexposed portion of the resist film 12 and having a line width of 0.09 μm is formed as shown in FIG. 13B.
However, as shown in FIG. 11D of Conventional Example 1 and FIG. 13B of Conventional Example 2, each resist pattern 2a or 12a obtained by the conventional pattern formation method is in a defective shape.